The present invention relates to a signal and power applying unit for use with a memory cassette containing therein a semiconductor memory and removably attached to an adapter mounted on the body of a numerically controlled machine tool.
Memory cassettes with semiconductor memories incorporated therein have recently been put to use as an external memory for storing a program and its data, and have come to see as wide an application as magnetic tape cassettes. The memory cassette is advantageous in that data does not need to be modulated and demodulated when written into or read out of the memory cassette, and no drive mechanism is required. Therefore, the stored data in the memory cassette is highly reliable, the memory cassette is small in size and is less likely to fail during operation.
The memory cassette is connected by connectors to an adapter mounted on a numerically controlled machine. A program and its data stored in the memory cassette can be loaded into a memory in the numerically controlled machine through the adapter under the control of a read command issued by the numerically controlled machine. Usually, the memory cassette has no power supply of its own for energization, but is supplied with electric power through the adapter from the numerically controlled machine. The adapter and the memory cassette are mechanically coupled for electric connection by the connector, which comprises male and female interfitting connector members. Since the male and female members are normally manually coupled or disengaged, contact pins of the male member are brought into and out of contact with the receptacles of the female member at different times. Prior to connection of the memory cassette, the power supply on the adapter connector member has already been switched on with a voltage applied to the contact pins on the adapter connector member, and an interface signal between the memory cassette and the adapter has been in an active state. When the memory cassette is to be connected to the adapter, connection of the contact pins at varying timing can apply the power supply voltage through a bypass or leakage route to the semiconductor memory, which is then can be destroyed. More specifically, the voltage may be applied to the semiconductor memory through a contact pin at the instant a contact pin leading to a 5-V power supply is connected while a ground pin is not yet connected. This applied voltage accidentally erases a stored program, or destroys the semiconductor memory.